It is known to employ fluid bed reactors in wastewater treatment facilities. A liquid to be treated, such as wastewater or water polluted with volatile organic constituents, is conducted upwardly through a bed of particles, such as granular activated carbon, contained in a fluid bed reactor. The liquid is conducted through the bed of particles at a rate sufficient to cause fluidization of the bed. The particles serve as carriers for growth of biological material that is provided in the bed of particles and that acts on the liquid.
For example, the biological material can be bacteria in the form of denitrifying biota which denitrifies wastewater. Alternatively, the biological material can be microorganisms that consume volatile constituents in the liquid. In this case, the microorganisms either immediately consume the volatile constituents, or the volatile constituents are absorbed by the particles until they can be consumed by the microorganisms.
The biological material grows and causes the bed to expand. Means are provided for removing excess biological growth.
Attention is directed to the following references which relate to fluid bed reactors and which are incorporated herein by reference:
______________________________________ U.S. Pat. No. Inventor(s) Issue Date ______________________________________ 4,961,854 Wittmann et al. October 9, 1990 4,800,021 Desbos January 24, 1989 4,469,599 Gros et al. September 4, 1984 4,464,262 Owens et al. August 7, 1984 4,322,299 Scholten et al. March 30, 1982 4,250,033 Hickey et al. February 10, 1981 4,202,774 Kos May 13, 1980 4,182,675 Jeris January 8, 1980 4,177,144 Hickey et al. December 4, 1979 4,009,105 Jeris February 22, 1977 4,009,098 Jeris February 22, 1977 3,956,129 Jeris et al. May 11, 1976 3,846,289 J. S. Jeris et al. June 19, 1972 2,786,801 J. B. McKinley et al. March 26, 1957 1,139,024 Leslie C. Frank May 11, 1915 ______________________________________
Attention is also directed to Japanese Kokai Patent No. Sho 57(1982)-122997, Shimodaira et al.
Liquid to be treated can be supplied to the fluid bed reactor via an equalization surge tank, which accommodates changes in flow rate and concentration of influent, which supplies liquid to the fluid bed reactor at a constant rate, and which optionally includes a stirring or mixing device.
In wastewater treatment facilities of the type including a fluid bed reactor, it is desirable to control iron fouling caused by the presence of ferrous iron in the liquid being treated, and caused by the presence of iron metabolizing bacteria, in the fluid bed reactor. Previously, iron fouling has been allowed to occur until there is an interference in the operation of the treatment facility--e.g., high pressure drops, maldistribution of water at the bottom of the fluid bed reactor, or a poorly fluidized bed. Iron metabolizing bacteria are a major contributing factor in iron fouling. It is desirable to reduce iron fouling without producing gaseous emissions containing stripped volatile organic constituents.
A similar problem exists when attempting to clean an underground storage tank area by pumping groundwater into the area and then conveying water from the area to a fluid bed reactor for treatment. The groundwater which is pumped into the area might be high in iron content, and might cause fouling of the fluid bed reactor.
Prior methods for removing iron from waste water, in an effort to reduce iron fouling, have included ion exchange, addition of sequestrants, aeration towers, or use of iron filters. These methods are more complex and more expensive than the method employing the invention disclosed herein. Further, these methods may create iron sludge which must be disposed, and these methods are potentially hazardous if the iron is removed upstream of the treatment process that employs the fluid bed reactor, particularly if volatile components are being carried by the wastewater.
Devices for dissolving gas in liquid are known. Attention is directed to the following references which are incorporated herein by reference:
______________________________________ U.S. Pat. No. Inventor(s) Issue Date ______________________________________ 4,507,253 Wiesmann March 26, 1985 4,466,928 Kos August 21, 1984 4,412,924 Feather November 1, 1983 4,246,111 Savard et al. January 20, 1981 3,926,588 Speece December 16, 1975 3,804,255 Speece April 16, 1974 3,643,403 Speece February 22, 1972 ______________________________________
None of the above references relating to dissolving gas in liquid teach or suggest a method of reducing iron fouling in a water treatment facility of the type employing a fluid bed reactor. Attention is also directed to copending U.S. patent application Ser. No. 07/972,742 which is assigned to the assignee of the present application and which is incorporated herein by reference.